Howdy,
My 89 YJ with a 258 runs like crap (random missing and coughing) at 1500+ RPM.

The engine is all stock, Carter BBD. I live in CA, so removing the BBD is not a smog legal option.

FYI, I first noticed this about a week after I bought the jeep, I’ve been living with the problem for about a year, but now it is time to get the thing smoged so I gots to fix it.


The engine starts easy and idles fine ( might be a little high, 800 RPM) the little metering valves in the BBD move and stay centered during idle.

But when I step on the gas (in gear or out of gear) and try to maintain an RPM, above 1500 RPM the engine sputters and misses. Up until I put a TFI coil ( and the wider cap’n rotor )on it would do this right at idle. Now with the TFI coil it behaves the same but only shifted higher in the RPM range. If I disconnect the EGR, it runs much better. But, it pings. I tried a new EGR but it made the missing worse.

I also replaced the fuel pump and the fuel filter. Plugs, wires….

I tried increasing the RPM while watching the metering pins in the BBD carb and they start to move forward as the RPM is held and eventually bottom out. I think that this represents a lean condition or a vacuum leak. But, why doesn’t it run lean at idle?


Any ideas that don’t envolve tossing the BBD are welcome.

Sounds common. Time for an engine swap. I had similar trouble with my 258. I swapped in a V-8.

Yeah, and that will solve his smog issues how?

One of the few things I love about Michigan, no smog laws, but you guys get all the good trails, so I'd rather smog my junk.
Have you thought about the cam being rounded out? That will cause some really bad popping and missing and no power above idle, but if you've been living with it for a year it would be total junk by now. Try the old "spray carb cleaner at all the hoses and the sides of the carb" while holding it at 1500 or so, see if it clears up, maybe a vacuum leak or bad carb throttle shaft bushings.

have you checked the timing?

I've checked it at idle. i set it to 9 BTC. why do you think timing would be a issue?

do you think I'm getting to much advance?...

the mechanical advace springs feel springy when I checked the distributer shaft for play.

btt

Mine just started missing, the SLIGHTEST little bit, at right around 1500 RPM's. I've got 200,300 miles on my original motor. I don't know what your mileage is like right now, but Id wouldn't be too upset if I ended up having to rebuild my motor soon.
Scott